The present invention generally relates to data communication control methods employed in radio control apparatuses in mobile communication systems, and, more particularly, to a data communication control method for reducing interference among different communication systems without a deterioration in the data throughput characteristics.
The present invention also relates to a radio control apparatus that employs the above data communication control method, and a mobile communication system that includes the radio control apparatus.
In a case where the frequency band areas used by two communication systems utilizing different communication methods are close to each other, interference might be caused between the two communication operations.
In a W-CDMA/FDD technique that applies a FDD (Frequency Division Duplex) technique to a W-CDMA (Wideband-Code Division Multiple Access) technique, a frequency of 1,920 to 1,980 MHz is used for uplink transmission, while a frequency of 2,110 to 2,170 MHz is used for downlink transmission. In a W-CDMA/TDD technique that applies a TDD (Time Division Duplex) method to the W-CDMA method, the same frequency of 2,010 to 2,025 MHz is used for both uplink transmission and downlink transmission.
As described above, the uplink frequency band area of the W-CDMA/FDD technique is relatively close to the frequency band area of the W-CDMA/TDD technique. If a base station of one of the two communication systems is located in the vicinity of a base station of the other communication system, interference might be caused between the two communication operations through those base stations. Such an undesirable satiation can be prevented by employing a filter that reduces signal components outside a predetermined frequency band area.
Meanwhile, in a case where a mobile station utilizing the W-CDMA/FDD technique and a mobile station utilizing the W-CDMA/TDD method are located in the vicinity of each other and performing communication, the uplink communication by the W-CDMA/FDD technique might interfere with the downlink communication by the W-CDMA/TDD technique.
The interference is naturally caused in a dual mobile station that is compatible with a dual mode utilizing both the W-CDMA/FDD technique and the W-CDMA/TDD technique as communication systems, especially when the system utilizing the FDD method and the system utilizing the TDD method are used at the same time (this operation will be hereinafter referred to as a “multi call”).
The interference can be avoided by improving the filtering performance of each of the W-CDMA/FDD transmission and reception devices and the W-CDMA/TDD transmission and reception devices so as to prevent generation of spurious signals or noise outside a predetermined band area and to minimize adverse interaction.
However, a filter that can realize excellent shutoff characteristics generally requires a large number of elements. This of course results in an increase of power consumption and an increase of size of the entire device. As there is an increasing demand for smaller mobile stations that consume less energy, it is difficult to employ such a filter as described above. Also, this problem apparently becomes more noticeable in a dual mobile station that includes transmission and reception devices of both methods.
In an attempt to reduce interference with no improvement in filtering performance, Japanese Patent Publication No. 2,830,914 discloses a method of controlling data transmission and reception timing so as to reduce interference. More specifically, the disclosed method involves VOX (Voice Operated Transmitter) control at a mobile station. Under the VOX control, a communication operation utilizing one of the two communication methods enters a transmission OFF state, and data transmission and reception are performed utilizing the other communication method while the other radio wave transmission and reception are suspended.
Here, the VOX control is a transmission output control operation that is to be performed while audio signals to be used for reducing power consumption at the mobile station are being input, and is performed to transmit encoded audio signals only in audible periods and to stop radio transmission in silent periods (see page 263 of “Digital Mobile Communication”, supervising editor: Moriji Kuwabara, published by The Science News Ltd.).
The above data communication control method disclosed in Japanese Patent Publication No. 2,830,914 has the following problems.
First, in a case where one of the communication systems is performing data transmission and reception while the other communication system is not performing radio wave transmission and reception, the data to be transmitted or received by the other communication system may not be properly received due to interference when the former one of the communication systems resumes the radio wave transmission and reception. After demodulating reception signals, a mobile station normally requests for resend of lost data if there is any. As the amount of data loss due to interference increases, more requests for resend are issued. Frequent resending operations result in a rapid decrease of the throughput in the other communication system.
Secondly, some users may have a high ratio of the audio data transmission time to the entire communication time. In such a case, the transmission OFF period under the VOX control is very short, and accordingly, data transmission and reception might not be efficiently performed. As the accumulated transmission data cannot be promptly transmitted, the throughput of the data rapidly decreases.